Titanium is the 5th most abundant metallic element on earth.
Properties of titanium, such as high-strength, lightweight, excellent corrosion resistance, and high temperature operation, make it suitable for use in a wide range of engineering applications. These properties suggest that titanium is more suitable for use in many engineering applications in which engineering steels (such as austenitic stainless steels) and aluminium alloys (such as high strength aluminium alloys) are currently used.
However, world titanium production is currently only around 80 KT per year, a very small amount compared to the annual production of stainless steels and aluminium alloys.
Titanium consumption is low due to its high cost. This is attributable to the (a) complicated process of refining ore sources (rutile and ilmenite) into titanium and titanium alloys, and (b) high production costs associated with pyro-metallurgical and electro-metallurgical production of plates, sheets and other semi-finished titanium and titanium alloy products.
FIG. 1 illustrates schematically the different stages involved in manufacturing titanium or titanium alloy plate and the relative costs that each of the individual manufacturing stages contribute to the overall product costs.
Based on current manufacturing costs, if it was possible to reduce the cost of manufacturing semi-finished titanium or titanium alloy products by around 30%, then products like titanium sheet and plate would have the potential to displace other structural engineering metals, in particular austenitic stainless steels and high-strength aluminium alloys, from many of their current areas of application, such as shipbuilding, aircraft manufacture, and chemical process industries. Consequently, such production cost reduction could open up a market of more than 1 MT of titanium metal per year.
As is evident from FIG. 1, the manufacturing stages that provide the biggest potential to achieve cost savings are the semi-finished product (eg plate) fabrication stage (which contributes around 50% to overall production costs) and the titanium production stage (with oxide reduction and electro-metallurgical metal melting contributing around 40% to overall costs).
Commercial scale titanium production relies currently exclusively on the Kroll process. This process involves, in short, (a) purification of the base titanium dioxide ore to remove compounds other than titanium dioxide and other titanium oxides, (b) chlorinating to form titanium tetrachloride in the presence of a reducing agent, (c) purifying the tetrachloride, and (d) subsequently reducing the tetrachloride to metallic titanium using magnesium (or sodium) in a neutral argon or helium atmosphere. The Kroll process produces titanium in the form of a highly porous material, termed titanium sponge, which commonly has impurities such as oxygen, nitrogen, carbon, and hydrogen. The sponge titanium is subsequently crushed and melted (in an inert atmosphere) into ingots for further processing.
Scientific and patent literature, including patent literature of the applicant, discloses that it is possible to produce high grade titanium directly from commonly available and abundant titanium oxides using an electrochemical method as an alternative to the currently employed Kroll process.
The present invention was made during the course of an on-going research project on the electrochemical reduction of titanium carried out by the applicant.
In the course of the research project the applicant has manufactured titanium oxide pellets and conducted electrochemical reduction experiments on the pellets that confirm that it is possible to produce 99.9% and higher purity titanium. The applicant has identified method parameters that require consideration in scaling up the experimental electrochemical cells into pilot plant and commercial plant operations and the electrochemical reduction method that is characterised by these parameters is the subject of other patent applications of the applicant.
Investigations conducted by the applicant in relation to the cost structure and energy consumption of a scaled-up plant that uses the electrochemical reduction method of the applicant rather than the conventional Kroll process suggest that the cost reduction potential of the electrochemical reduction method is about 30%, which amounts to an overall production cost reduction of about 10%.
Whilst such cost reduction potential might of itself be sufficient to justify full scale electrochemical reduction plants for the production of titanium, it is not sufficient to promote higher consumption of titanium as a replacement for the above mentioned conventional engineering metals.